Is the new T1 category as defined in the eighth edition pancreatic cancer staging system an improvement?

Abstract

Introduction: The new T1 pancreatic cancer by the eighth edition of the American Joint Committee on Cancer staging system discards the concept of “extension beyond the pancreas” and focuses on size only. Furthermore, it is subdivided into T1a, T1b, and T1c based on size. These changes have not been evaluated. The aim was to evaluate the feasibility of the new T1 definition in the pancreas head cancer cohort. Method: A multinational cohort study was conducted. Data from 540 patients with T1 pancreatic ductal adenocarcinoma as defined by the eighth edition were collected from three tertiary centers in Korea, Japan, and the USA. Invasive intraductal papillary mucinous neoplasms were excluded. Survival analyses were performed. Result: Among 540 patients, 181 patients were T1 according to the seventh edition and 359 were down-staged to T1 from the former T3 because the concept of “extension beyond the pancreas” was discarded. The 5-year survival rate and the median survival of T1 patients were 30.6% and 27 months, respectively. Comparing tumors that extend beyond the pancreas (new T1) and those confined within the pancreas (original T1), the latter showed longer median survival (43 vs. 24 months, p<0.001). In terms of T1a/b/c, there were no significant differences in survival. Using MaxStat, subdividing into two groups using 1.1 cm as the cut-off value yielded discrete prognostic groups (p<0.001). Conclusion: The new T1 definition may be more practical, but the implications of the concept of “extension beyond the pancreas” should be re-investigated. Further, the subcategorization of T1a/b/c may not be adequate and may require revision or deletion.